A writing instrument with a cap can have a shaft on one of whose ends a moist tip is mounted and a circular bulge on the shaft adjacent to it.
The cap can have an elongated jacket which is pushed onto the shaft and in which an axially slidable sealing insert is mounted which contains at one end an open tubular sleeve shaped portion for insertion of a writing tip.
On pushing of the writing tip into the tubular sleeve-shaped portion, the circular bulge acts as a seal for the writing tip in a moist chamber. A compressible spring is provided by which the sealing insert is shiftable relative to the jacket in the direction of the writing instrument.
The sealing insert and the jacket have contacting stops to limit their opposite relative movements. The cap also can have a signal slider which is mounted in the end of the cap opposite to the writing instrument and is slidable out of it depending on the position of the sealing insert and in a locking configuration which holds the writing tip in the sealing insert.
A writing instrument with a moist point, for example, a fountain pen, a felt tip pen or the like, when it is stored covered with a cap as just described, should be sealed in a moist chamber surrounding the point in order to prevent drying out of the tip.
Particularly with a felt or fiber writing instrument, the capillaries between the fibers forming the writing tip quickly dry out and plug up and thus the flow of ink from the writing instrument is prevented so that the writing instrument, although it still may contain sufficient ink, can no longer be used and either must be cleaned with considerable effort or, as is frequently the case, is discarded.
Thus it is important that a proper seat of the cap on the writing instrument after each use be guaranteed.
There have been numerous suggestions for solution of this problem which are much too expensive for use directly with a disposable writing device, although they may be applicable in a complicated and expensive writing instrument structure.
One known writing instrument with a cap is described in U.S. Pat. No. 1,838,543 and is a fountain pen with a removable cap. Near the tip of the fountain pen a circular bulge is located on its shaft and a jacket is mounted inverted on the shaft which surrounds the circular bulge with clearance.
Inside the jacket an axially slidable sealing insert is mounted which has a tubular sleeve like portion open to the writing instrument which is surrounded by small spring clips which extend longitudinally. The ends of the spring clips facing the fountain pen are bent inwards. A compressible spring mounted between the jacket and the sealing insert presses the sealing insert in the direction of the opening of the jacket.
On the inner wall of the jacket a circular groove is formed. When the opening of the sleeve-like portion of the sealing insert facing the mouth of the jacket reaches this circular groove, the spring clips can spread to the outside and engage with their ends in the wall of the circular groove so that the sleeve is held in this position.
If the fountain pen is pushed into the jacket, its circular bulge comes into contact with the mouth of the sealing insert and can be pushed deeper into the jacket. Thus the spread out spring clips are bent back and engage under the circular bulge with their inwardly bent ends so that the bulge is gripped securely and pressed against the mouth of the sealing insert and of course so that a seal is attained.
The end of the jacket facing away from the writing instrument is closed and has an axially movable signal slider which is pressed upwards by a single coil spring. The inner end of the signal slider is provided with lock catches which contact the ball-shaped end of the signal slider inside the jacket and can engage a pin coaxial to it which is connected to the spring clips.
If the sealing insert is pushed all the way into the jacket a locking engagement with the end of the signal pin occurs. After loosening the shaft of the writing instrument it is pressed out from the jacket slightly with the sealing insert so that the signal slider is drawn into the ejected end of the jacket. A drawn in or retracted signal slider indicates that the mounting of the circular collar in the mouth of the sleeve is prevented while an extended signal slider indicates the opposite condition.
Essentially the known writing instrument functions as follows: upon putting of the jacket on the writing instrument the seal between the sealing insert and the moist chamber is made, but first this condition is indicated by the signal slider. On removing the jacket from the writing instrument, first a signal of that state in which the cap is removed is given and only then is this condition realized. Thus it is guaranteed that a timely signal is provided.
This great advantage is however achieved at great expense and requires a complicated structure. Moreover the known mechanism is not completely reliable: upon an erroneous insertion of the writing instrument into the jacket or on upon the bending of one of the spring clips there is the danger that the circular bulge will not enter the mouth of the sleeve but will engage an inwardly bent end of a clip spring.
In this case the sealing insert is pushed onto the jacket, the clip spring assuming its engaged position and the signal slider indicating a sealed condition without any real engagement between the sealing insert and the writing instrument occurring. The circular bulge then does not lie claw between the mouth and the claw-like end of the clip spring, but outside of this region.
In order that the operation of this known instrument not be impaired, the jacket must be slidable against the shaft with comparatively large play. Now only an inadequate seal between the circular bulge and the mouth of the sleeve occurs, so that the eventual drying out of the writing tip cannot be prevented.
From the German Open Patent Applications Nos. 34 01 739 and 34 41 435 writing instrument caps are known which have a sealing insert slidable in a longitudinal direction which is movable over the writing instrument, the writing instrument being inserted against friction in a tubular sleeve-shaped portion of the sealing insert or withdrawable out from it. In the sealing insert a signal pin is mounted which is detectable when the insert is completely shoved onto the writing tip. The axial motion of the sealing insert is controlled by a limited locking force which is designed that the limited force is smaller in unlocking and greater in locking than the frictional force to be overcome in sliding in or pulling out the writing tip.
When with the known writing instrument as a result of use or because of an unwanted lubricant the frictional force is reduced on pulling out the writing tip so that the above named relationships are not maintained, it can not be guaranteed that the sealing insert will remain in its position facing away from the opening of the cap after the writing tip has been drawn out. The signal pin thus may indicate erroneously a sealed seating of the writing instrument in the cap.
German Utility Model DE-GM No. 73 14 439 describes a fountain pen which has a sealing insert into which the shaft of a writing instrument can be pushed. The writing instrument is provided with a circular bulge which is engaged by a corresponding sealing surface of the sealing insert with the writing instrument inserted. An indication of the sealed seating of the writing instrument is not provided with the known cap used in this fountain pen.
German Utility Model DE-GM No. 72 22 646 relates to a locking cap of a fountain pen in which the cap or its jacket locks on the shaft of the writing instrument. A circular groove is provided on the shaft which cooperates with a corresponding locking strip on the upper surface of the cap or the jacket.
A similar locking between a writing instrument cap and a shaft is provided in German Utility Model DE-GM No. 69 11 249 wherein the shaft of the writing instrument is provided with a circular bulge and the inside of the cap with a corresponding opposing groove.
German Patent DE-PS No. 827 760 involves a fountain pen with a cap which is screwed on. The closing cap contains an axially slidable sealing insert. The sealing insert is kept under tension by a spring in the direction of the open end of the cap. An indication as to the state of the seal of the writing instrument tip is not provided in the three last-mentioned writing instruments.